While human patients and healthy subjects are being imaged at 3T, 7T, 8T, 9.4T and soon, 11.74T, more data and understanding of RF safety at these ultra-high field strengths is needed. The overall objective of this proposal therefore is to investigate high frequency RF heating in order to improve RF safety for high field MRI. Safety will be better assured by developing the means to accurately predict and measure RF heating contours in human anatomy. These means will be achieved by accomplishing the following aims. First, a more fundamental understanding of the electrodynamic and thermodynamic nature of RF induced heating and heat transfer in anatomy will be furthered through mechanistic derivation and modification of the empirical Pennes Bioheat Equation. Second, this new theoretical model will be tested at high field Larmor frequencies by invasive, direct measurement of RF heating in anesthetized porcine models, by fluroptic thermometry. The porcine model is required as an intermediate step toward understanding and measuring RF heating in humans. Toward this end, the third aim is to develop a noninvasive NMR thermometer that is calibrated to an absolute temperature scale by the invasive fluroptic measurement. Once confidence is gained in predicting and noninvasively measuring temperature in pigs, these methods will be applied to monitoring RF heating in humans and so accomplishing the final aim of this study. With new understanding, data, and thermal measurement methods, high field human MRI will become safer.